1. Field of the Invention
The present invention relates to the purification of acetonitrile and particularly to the removal of hydrogen cyanide and water from acetonitrile by contacting the nitrile in one or more steps with a concentrated alkali metal hydroxide.
2. Description of the Prior Art
Numerous processes have been disclosed for the purification of acetonitrile many depending upon the desired use of the acetonitrile. U.S. Pat. No. 3,328,458 issued on June 27, 1967 discloses the removal of water and hydrogen cyanide from acetonitrile by first contacting the nitrile with a drying agent such as calcium chloride, sodium sulfate or alumina and a compound which may be used in combination with the aforesaid drying agent to produce a soluble cyanide salt such as copper acetate or silver nitrate. U.S. Pat. No. 3,203,974 issued on Aug. 31, 1965 discloses the removal of pyridine from acetonitrile by contacting the nitrile with acids and acid anhydrides which are formed by the combination of oxygen and a normally solid element of Groups III, IV and V of the Periodic Table, e.g., boric acid, phosphoric acid and stanic acid.
An elaborate technique for azeotropic distillation of acetonitrile to remove water, hydrogen cyanide, acrylonitrile, acetone and higher boiling nitriles is disclosed in U.S. Pat. No. 3,451,899 issued on June 24, 1969. Acetonitrile purification by reacting the crude acetonitrile with alkali metal and ammonium hydroxide, ammonia and aliphatic amines at a temperature between 50.degree.-212.degree. F. to form a reaction mixture in which the hydrogen cyanide and acrylonitrile transform into compounds of higher molecular weight and the resultant material fractionally distilled to recover pure acetonitrile is disclosed in U.S. Pat. No. 4,119,497 issued on Oct. 10, 1978.
Acetonitrile can be dehydrated by the addition of methylene chloride, subjecting the thus formed mixture to stratification to separate an aqueous upper layer, and fractionally distilling the water in the methylene chloride from the lower layer as a binary azeotrope according to the teachings of U.S. Pat. No. 2,453,472 issued on Nov. 9, 1948.
Alkaline media, e.g., sodium hydroxide, have been employed as a part of purification processes. East German Pat. No. 110,489 published on Dec. 20, 1974 combines discontinuous azeotropic distillation with acrylonitrile to dry the acetonitrile followed by heating the distillate in an alkaline medium up to 90.degree. C. to permit decomposition of impurities and further distillation. Acetonitrile water azeotrope is taken overhead and decomposition products of acrylonitrile and hydrocyanic acid are removed in the tails.
Titratable cyanides and acrylonitrile in acetonitrile have been converted to sodium cyanides and succinonitrile respectively by the addition of sodium hydroxide followed by the addition of ferrous sulfate to convert sodium cyanide into sodium ferrocyanide. Distillation is then used to recover acetonitrile having a low cyanide content (Japanese Pat. No. 7235416 published on Mar. 23, 1962). Dilute sodium hydroxide has been disclosed as a catalyst for the cyanoethylation of acrylonitrile contained in acetonitrile, e.g., in French Pat. No. 1,431,919 issued on Mar. 18, 1966.
It is also known that concentrated caustic causes nitriles to hydrolize [Kirk, Othmer, Encyclopedia of Chemical Technology, Vol. 9, pp. 356-7 (19)] which reaction has been taught to be undesirable in the purification of acetonitrile [Pure & Applied Chemistry, 13 429-431 (1966)].